How to enable animation of linked rigged object
you have to use the Proxy Objects :

A proxy is a legal stand-in or substitute for the real thing. In Blender, when you make a linked copy (described above), you cannot edit the object; all you have is a link to it. You cannot add to it or change it, because its source is in another file that is not open.   Blender Manual


to convert the linked object into a Proxy Object you select the linked Object and hit Ctrl+Alt+P now you can animate the proxy object and it will get updated to the linked when you reload the file.